Condenser



Sept. 15, 1925.

1,553,549 w. H. PRlEss CONDENSER Filed April 3, 1920 2 Sheets-Sheet l Sept. 15, 1925.

W. H. PRIESS coNDENsER 2 sheets-sheet 2 Filed April 3, 1920 PatentedSept. 15, 1925,v

UNITED ySTATES PATENT oFFlciz.

WILLIAM H. PRIESS, OF NEW YORK, N. Y., ASSIGNOR TO' WIRELESS SPECIALTY APPA- RATUS COMPANY, OF BOSTON, MASSACHUSETTS, A CORPORATION OF NEW YORK.

coNnENsER.

Application led April 3,

To all whom 'it may concern:

Be it known that I, WILLIAM H. Pninss, a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented certain Improvements in Condensers, of which the following description, in connection with the accompanying drawings, is a'speciication, like reference characters on the drawings indicating like parts in the several figures.

This invention relates to electrical condensers and it has among its objects to devise a simple, compact and eiic'ient construction which can be economically manufactured, and which will be adapted for use in many classesof service.

The conducting and dielectric elements of a condenser are practically always secured. together with a thin film of some kind of adhesive material, such as wax, varnish or the like, and it is important from the standpoint of securing maximum condenser efliciency and avoiding the danger of a break down in the condenser, that the presence of air, vapor, or an excessive thickness of adhesive material between the elements of the condenser be eliminated. Accordingly, it is onev of the objects of the present invention to devise a condenser construction with which this result can be conveniently ac-A complished.

Tue nature of the invention will be readily understood from the following description when read in connection with the accompanying drawings, in which-'- Figure 1 isa cross sectional view of a condenser constructed in accordance with this invention;

Fig. 2 is a plan view of the condenser shown in Fig. v1 with the cover plate removed; and

Fig. 3 is a View similar to Fig. 1 of a modified construction.

The construction shown in Figs. 1 and 2 comprises a condenser stack consisting of a series of condenser units 2 connected to-l gether in the desired relationship with suitable mica separators 8 between the units and insulating members 4 and 5 at the opposite ends of the stack. These condenser units may be made according to any convenient process and are built up of alternating sheets of dielectric andfoil. Preferably the condenser stack is assembled and the lead 1920. Serial No. 370,992.

strips 6 and 7 secured thereto before it is placed in the metal casing 8 in which it is to be permanently enclosed.

One end of the stack rests or bears on a metal plate 9' secured'to the casing by screws and in order to apply the desired pressure to the stack, a pressure plate 10, preferably of metal, is placed against the opposite end or top of the stack, with av spring plate 12 on top of' the plate 10 and a thicker plate 13 is superposed on the spring plate 12. The plate 13 is provided with two depressions to receive the rounded ends of screws 14.-14 which are threaded through the thickened portion of one wall of the casing 8. It is obvious that by turning these screws in the proper direction an exceedingly heavy pressure may be applied to the stack and, due to the character of they plate 12, this pressure will be resiliently maintained. The spring plate preferably is-.` made of spring steel and is curved or sprung longitudinally .to enable it to exert the desired spring action. A lug or pin 15 may be used to locate the spring plate relatively to the plate 10. Since the pressure exerted on the stack is transmitted through the op-` t posite walls of the casing it is necessary to make the casing sulliciently strong to resist this strain, but this requirement does not necessitate the use of an excessively heavy l casing.

It is usual to heat or bake a condenser stack while it is under pressure for the purpose of reducing to a minimum the presence of air, gas, vapor or the thickness of the adhesive material between the elements of the condenser and also, in the case of a condenser in which varnish is used as the adhesive, for the additional purpose of driving out any solvent still remaining in the varnish. In some types of condensers it may be more convenient to perform this baking operation before the condenser stack is placedin the casing 8. In other types, however, it is preferable to assemble the parts in the casing as shown in the drawing and then heat or bake the condenser while pressure is applied to the condenser stack by means of the screws 1li- 14. These screws 14-14 preferably are made longer than is necessary for the finished casing and they are provided with heads similarto a bolt head so that a -good purchase can be obover the opening in the casing by means of screws. Prior to the fastening of this cover in place, however, the conducting lead 6 from one end of the condenser stack is soldered to a terminal screw 17 and the screw is placed in a hole provided for it in the cover 16 and is secured therein by a nut 18. The lead 7 from the opposite end of the condenser is secured to the casing by a screw 19, the casing constituting a terminal. It is obvious, however, that if desired both terminalsof the condenser could be brought to binding posts on the cover 16. It is obvious also that if desired the space in the casing surrounding the condenser stack lcould be filled with wax or other suitable insulating material.

A' somewhat diiferent embodiment of the invention is disclosed inFig. 3 in which the parts corresponding t those of the embodiment shown in Figs. 1 and 2 are designated by the same numerals as those used in the latter igures except that these numerals are primed. It will be seen that the condenser stack is mounted in the casing in the same manner as in Figs. 1 and 2, the stack resting on a plate 9 at one end of the casing and pressure being applied to it through a spring plate 12', and screws 14-14 threaded throu h one wall of the casing. In this construction, as in thatpreviously described, the casing forms, in effect, a yoke or clamping member which resists the thrust exerted on the stack. The plate 9 preferably is provided With two lugs, one of which is shown at 20, which bear against the inner surface of the cover 16 andv prevent the plate from slipping out of its proper position. The cover plate is secured to the casin 8 `by screws 21-21, the heads o f which bear on pressure distributing plates 22-22 set into the cover. In this form of the invention the high potential terminal 23 mounted in insulating cover 16 is connected by the lead 6 to Vthe middle or hi h potential. part of the condenser stack an the leads 7 fat the opposite low potential endsof the stack are 6', is closed by a plate 24 secured in place by screws, a suitable gasket being interposed between the plate and the casing.

This condenser casing is designed .to be filled with insulating material such as wax and the construction here provided is of' particular advantage in performing the waxing process. That is, after the stack has been assembled in the casing in the positiony shown with the cover 16 and terminal 23 in place, with lead 6 connected to the terminal, the casing is inverted, filled with molten wax, and the stack is heated up to a point abovethat necessary to maintain the wax in molten condition, usually about 135O to 145 C. Vhile the stack is maintained at this temperature the screws 14-14 are turned up far enough to apply the desired pressure tothe stack. This squeezes out the surplus wax frombetween the layers and brings the alternate layers of mica and tin foil into very intimate contact. The wax is then allowed to cool and solidify within the casing. After the waxing process has been completed the plate 24 is secured in position. This construction thus has the advantage that it secures a thorough waxing of the parts adjacent to the high potential terminal which are the points subjected to greatest strain in the condenser.

It will now be evident that this invention provides a very simple condenser construction in which the manufacturing operations can be conveniently and economically performed and which, with the proper selection of materials and the exercise/of reasonable care in the process of manufacture, will provide a very efficient and reliable condenser.

VIn one of the forms above described, the condenser units have been shown connected in series, while in the other form the two halves of the condenser are in multiple, and the sections in each half are connected in series. It is obvious, however, that any desired arrangement of connections can be employed. It will also be appreciated that the form of the invention illustrated in Figs. 1 and 2 provides a very convenient unit for connection externally either in series or multiple as particular service conditions may require.

The clamping means for the stacks of the present invention comprises means at one end of the stack for receiving and opposing a thrust exerted or applied at the opposite end of the stack to compress the elements of the stack. Specifically I utilize the casing 8 or the block or member 9, 9 for receiving the thrust at one end of the stack, and a similar member, such as plate 13, 13 for applying or transmittinvr the pressure to the opposite end of the stac from screws 14, 14 threaded in the casing. For ensuring that the clamping means be springy or yielding under conditions of stack variation in length, I interpose a spring, which preferably is, although not necessarily, of a tween either end o the stack and either member 9, 9 or 13, 13', such spring being located preferably as illustrated between member 13, 13 and a pressureplate 10, 10', the latter preventing damage to the stack elementsby the spring. Upon the assembly of the condenser, rthe spring is'maintained under compression between one end ofthe stack and one member by means of the screws or other means 14, 14', with the sheets of the stack in intimate contact under spring pressure.

What is claimed as new is:

1. A condenser comprising a casing, a condenser stack mounted. in said casing,l a

' screw threaded through on wall ofthe casing and pressing the stack against the opposite wall 'of the casing, and a spring plate through which the pressure is applied to the l stack by the screw, whereby the pressure is through which the pressure of resiliently maintained on the stack for various lengths thereof during service and the degree of pressure' may be varied byff adjusting the screw for maintenance of the pressure for such various stack-lengths.

2. In a condenser, the combination of a condenser stack, a casing in which said stack is mounted, and means for maintaining permanent pressure on the stack, said means including a screw mounted in one of the walls of v,the casing, and a splring plate t e screw on the stack is transmitted and maintained for various lengths of the stack inservice.

3. A condenser 'comprisi a stack of sheets, a clamping member Iligor said stack, a spring plate interposed between said member and an end of the. stack, and means for centering and holding" said spring plate in position during service parallel to the sheets Lin the stack andI across the end thereof to maintain the desired pressure over the active areas of the sheets for various lengths of the stack during service. f

4, A condenser comprisin a stack of sheets, a clamping member or and a; spring plate interposed between said member and an end of the stack for transmitting' spring pressure to the stack from end to -end thereof; said spring e plate being of `metal and normally `bent and lying across the end of the stack parallel to the sheets thereof and during service being' more or less flattened by the clamping member to maintain the desired compression for various lengths of the stackk during 5. A condensercomprisin a stack comoil and dielectric, a clamping member extendin lfrom end to end of said stack, a spring i ate interposed betweenv said member an an end of the stack, and means' for adjusting the pressure, onfsaid stack, said spring plate beplate type as shown, be-

said stack,

ing of metal and normallylbent and lying across the end of the stack parallel to the sheets thereof and during service being more or less flattened by said clamping member to maintain the desired compression for various lengths of the stack during service.

6. A condenser comprising a stack of sections of sheets connected in series and having its ends electrically connected together to be at' the same potential and an interx'nediate point. of high potential, a metal clamping member extending from end to end of said stack, and a spring plate interposed between said clamping member and an end of the stack'in position parallel to the sheets of the stack and across the end of the stack, said spring plate being of metal and normally tending to bend but during service being more or less flattened by said clamping member to maintain the desired compression or various lengths of the stack during service.

7. A condenser comprising a stack of sections of sheets connected in series and having its ends electrically connected together to be at the same potential and an intermediate point of high potential, a metal clamping `member surrounding said stack, a pressure plate on an end of the stack, a spring plate interposed between said member and pressure plate, and means for adjustin the pressure on said stack, said spring p ate being of metal. and normally tending to bend but during service being more or less flattened between said clamping member and said pressure member and thereby' maintaining. a given pressure between the ends of Vthe stack for various len hs thereof during service, said pressure `ing distributed overthe areas of the sheets of the stack uniformly by means of said pressure member.

8. A condenser comprising a stack com- ,posed of alternate sheets of oiland dielectric, a clam in member` extending from end to end o said stack, a pressure plate on one end of the stack located parallel to the sheets thereof and distributing the pressure over the active areas of the sheets, and a lspring interposed between -said pressure lateand clamping member, said sprin ing arranged to be more or less contracted between said clam ing member and said pressure plate during service and thereby maintaining a given pressure between the ends ofthe stack for various lengths thereof during service.

9. In an electrical condenser, a stack com-l A,prising alternate sheets ofl vfoil and dielectric, a clam ing member extending from end to end of sald stack for maintaining uniform pressure over opposite ends of the stack, anda spring interposed lbetween said memvber and an end of the stack whereby said pressure is maintained resiliently, said spring during service yielding to lvarious sol lengths of the stack and thereby maintaining the desired pressure from end to end ot the stack.

10. In an electrical condenser, a stack comprising alternate sheets of foil and di-` electric, a pressure plate upon one end of the stack located parallel to the sheets in the stack and distributing pressure over the active areas of the sheets, a spring plate upon said pressure plate and also parallel to the sheets in the stack, and an all-metal clamping member surrounding said stack and plates and transmitting pressure to the opposite ends\o't` the stack through said sprin plate; said spring plate being of metal an normally tending to bend but during service being more or less flattened between the pressure plate and the clamping member by variations in the length of the stack, thereby maintaining the desired compression from end to end of the stack during service. 11. A condenser comprising a stack having parts at diiference of potential, a clamping member surrounding said stack and electrically connectedto a part at one potential,

the part of opposite potential being insulated therefrom, and a spring vplate interposed. between said clamping member and stack, said spring plate lying across the end of the stack parallel to the sheets thereoi and being of met-al and normally tending to bend `but during service being more or less flattened between the clamping member and the stack end by variations in the length of the stack during service, thereby maintaining the desired compression of the stack from end to end. v

12. In an electrical condenser, a stack, a

' casing constituting a clamp for said stack,

and means for exerting spring pressure upon the stack and interposed between the stack and casing and an end of the stack, thereby maintaining the desired compression while permitting variations in the length of the stack during service. l

13. A condenser comprising a casing, a condenser stack arranged horizontally within the casing, means including the sides of the casing for clamping the stack in place, a spring plate interposed between the end of the stack and said means, and means for centering and holding Asaid spring plate in position across the end of the stack parallel to the sheets therein; said spring plate being of metal normally tending to bend but during service being more or less flattened between the stack and said clamping means by variations in the length of the stack, y thereby permitting such variations while permitting maintenance of pressure by said clamping means.

14. A condenser comprising a casing, a condenser stack therein comprising alternate sheets of foil and dielectric, and spring pressure means acting against opposite walls of the casing to maintain the sheets of oil and dielectric in the stack under heavy spring pressure with the sheets in contact; said spring pressure means being constructed and arranged to permit variations in length of the stack during service while maintaining the desired pressure.

15. A'condenser comprising astack and spring clampincr means for said stack comprising a member at opposite ends of the stack, a pressure plate on an end of the stack and a screw threaded in said member and exerting atlirust against said pressure plate and the end of the stack to hold the stack under spring pressure from end to end in said member; said spring clamping means and pressure plate being constructed and arranged to distribute the pressure uniformly over the active areas of the sheets in the stack while permitting variations of the length of the stack during service.

16. A condenser comprising a stack of alternate sheets of foil and dielectric, and a spring clamp for the stack compressing the sheets in the stack into contact an/d constitutinga casing enclosing the stack; said spring clamp being constructed and arranged to distribute the pressure uniformly over the active areas of said sheets while permitting variations of the length of the stack during service.

17. A. condenser comprising a casing, a stack arranged horizontally within the casing, means cooperating with the casing and clamping the stack therein, and a spring plate interposed between said means and the stack to exert resilient pressure on the end of the stack and parallel to the sheets in the stack when under compression; said spring plate and clamping means being constructed and arranged todistribute the preslsure uniformly over the active areas of the sheets in the stack, and said spring plate being of metal normally tending to bend but in service being more or less attened toward the clamping means by variations in length of the stack.

18. A condenser comprising a casing, a stack arranged horizontally within the casing and engaging a wall thereof at one end, a pressure plate upon the opposite end of the stack, a spring plate engaging said pressure plate, a compression member engaging the spring plate, and a screw mounted on the casing and engaging the compression member for exerting spring pressure on the stack; said spring plate being of metal normally tending to bend but in service beingy more or less flattened between the pressurev plate and the compression member by variations in length of the stack, and said pressure plate and spring plate lying across the end of the stack parallel to the sheets therein and distributing the pressure uniformly over the active areas of said sheets.

tions. i

20. A condenser comprising a stack of sections connected in series and having parts ata dili'ei'ence of potential, a metal casing enclosing said stack and constituting a clamp therefor, said casing constituting a terminal connected to a part of one potential, a second terminal projecting through said casing and insulated therefrom and connected to a part at a different potential, and a spring plate interposed between the stack and casing; said spring vplate `being located parallel to the-sheets in the stack and across the end of the stack and being of metal normally tending to bend but during service being more or less {iattened by variations of length of the stack due to service conditions.

21. A condenser comprising a stack of sections 'connected in series and having parts at different potentials, a metal casing enclosing said `stack and constituting a clamp thereforfsaid clamp including means for exerting spring pressure over the stack, saidI casing constituting a terminal connected to a part of the stack at one potential, and a second terminalconnected to another part of the stack and projecting through said casing and insulated therefrom; said clamp being constructed andarranged to distribute the pressure uniformly over the area of the sheets in the stack While permitting variations of length of the stackv during service.

22, A condenser comprising a casing having a stackl therein, a terminaly projecting -through said casing and connected to said stack, the stack and casing being relatively proportioned to provide a space inside the casing around said terminal and the side of the stack and a filler of insulating material surrounding said stack and the part of said .terminal extending through said space, said casing being constructed with an opening located to permit introduction into said space of said filler in liquid form while said part' of the terminal is at the bottom of the liquid body; and a closure for said o ening for application after lthe introduction .of

. said filler. l

23. A- condenser'comprising a metal cas.- ing having` an insulating portion, a. stack of sections within said Acasing having a terminal electrically connected to said casing and a terminal projecting through the inholding it in position .wit

embedment of insulating material Within said casing and compacted around said. projecting terminal; said Acasing being constructed with yan opening located to permit introduction into said space of said embedment in liquid form While the part of said projecting terminal Within the casing is at the bottom of the liquid body; and a closure for said opening for application after the introduction of said embedment in liquid form.

24. A condenser comprising a metalcasing having an insulating portion, a stack clamped by said casing and positioned Within the saine, said casing being electrically connected to said stack, a second terminal from said stack projecting through lsaid in s ting portion, the stack and casing bei g relatively proportioned/ to provide a space inside the casing around said projecting terminal and the side of the stack and an embedment of insulating material around the stack and projecting terminal; said casing being constructed with an opening located to permit introduction into said space of said embedment in liquid form while the part of said projecting terminal Within the casing is at the bottom of the liquid body; and a closure for said opening for application after the introduction of said embedment in liquid form.

1 25. A condenser comprising a metal casing, a stack arranged horizontally Within said casing and electrically connected to said casing which thereby constitutes a terminal of the condenser and a second terminal projectin lthrough said casing and insulated there om, the stack and casing being relatively proportioned to provide a space inside the casing'around said projecting terminal and the side of the stack, an embedment of insulating material in the space and around the stack and projecting terminal, said casing being constructed with an opening located to permit introduction into said space of .said .embedment in liquid form While the part of said projecting terminal within the casing is at the bottom of the liquid body, and a closure for said o ningl for application after the introduction of ing a removable bottom portion, a stack .ar-I ranged vyithin the casing, means engaging the stac the casili a terminal connected to thel stack and fixe to and projectin through the top of the casing, and insu ating material fi ling the cas and compacted around said terminal, said opening through the bottom of the casthe stack for compressin iio iso.

ing when the removable bottom portion is removed permitting the introduction of the insulating material in liquid form into the casing inverted for the purpose so that said terminal may be at the bottom of the liquid body during the solidification thereof.

27. A condenser comprising a metal casing having an insulating portion, a stack4 arranged within the casing, the stack and easing being relatively proportioned to provide a space inside the casing around the sidesof the stack, means for clamping said stack, the thrust of said means and stack being taken u by the intermediate walls of the casing, t e 'opposite ends of said stack being at the same potential and connected to the casing constituting a terminal, a second terminal projecting through said insulating portion and electrically connected to an intermediate part the stack, said terminal also projecting through the space betweenthe stack and casing and being connected to the stack and an' insulating fillei within said casing and around saidisecond terminal and stack, said casing being constructed with an opening located to permit introduction into said space of said insulating filler in liquid form while the part ot-y said projecting terminal within the casing is at the bottom of the liquid body; and a closure for said opening for application after such introduction of the ller.

28. In an electrical condenser, a stack comprising sheets of conductor and dielectric, a sprin at one end of the stack and a member between which and an end of the stack the spring is located in service, said member being constructed and arranged to act by way of said spring to press the sheets in the stack from said end toward the other end thereofto maintain them in intimate `contact with one another under spring pressure throughout the length of the stack from end to end thereof; said spring and said member being constructed and arranged relative to the stack to act over the entire areas of thesheets in the stack and maintain the desired pressure while permitting-during service the lengthening and subsequent shortening of the stack.

29. In an electrical condenser, a stack comprising sheets of conductor and dielectric, a spring at one end of the stack, a member between which and an end of the stack the spring is located in service and means for maintaining said spring compressed between the end of stack and said member to hold the sheets in the stack compressed throughout its length from end to end thereof in intimate contact with one another under spring pressure; said spring i and said member being constructed. and arranged relative to one another and thel stack so as to act over the entire active areas of the sheets in the stack uniformly while permittingl the lengthening and subsequent shortening of the stack under service conditions.v

30. In an electrical condenser, a stack comprising sheets of conductor and dielectric, a pressure plate at one end of the stack, a spring abutting the ressure plate and a member between Whic and the pressure plate the spring is located, said member acting to compress the sheets in the stack throughout its length from end to end thereof to maintain them in intimate `Contact with one another under pressure of the spring against the pressure plate; said pressure plate being disposed across said ystack end parallel to the sheets in the stack to distribute the pressure uniformly over the active areas of such sheets; and said spring and said member being constructed and arranged relative to one another and the pressure plate so as to maintain the desired pressure while permitting variations in'length of the stack during service conditions.

31. In an electrical condenser, the com* bination with a stack of dielectric and conducting sheets, said stack being constructed to have a high difference of potential between its ends during service, of clamping means arranged to compress the stack from end vto end and hold the sheets thereof in intimate contact with one another during service while permitting variations of length of the sta-ck, said clamping means including a metal portion extending with metallic continuity .from one end of the stack to the other, and said clamping means including a metal spring plate ,arrangedtransversely of an end of the Astack and parallel to the sheets therein and normally tending to bend but during service being more or less flattened by the action of the rest of the clamping means 'whenvariations loccur in the length of the stack; and said clamping means including also an insulating ineans consisting of material capable of withstanding high compression and located between an end of the stack and an adjacent portion of the rest of the clamping means and thereby held under yielding compression and acting to prevent the spring plate of the clamping means from short-circuiting the ends of the stack; said metal spring plate. and insulating means of the clamping means being constructed and arranged to distribute the clamping pressure uniformly over the entire active areas of the sheets in the stack. i

32. In an electrical condenser, the coinbination with ay stack of dielectric and conducting sheets, said stack being constructed to have a high difference of potential between its ends during service, Vof clamping means arranged to compress the stack from end to end and hold'the sheets therein in intimate contact with one another while permitting variations of length of the stack during service, said clamping means including a principal portion of metal extending with metallic continuity from one end of the stack to the other; said clamping means including an insulating means capable of withstanding high compression and located between an end of the stack and an adjacent end of said metal portion and held under high compression thereby; and said clamping means including also a metal spring plate located between an end of the stack and said metal portion and extending parallel to the sheets in the stack and across the end of the stack to distribute the clamping pressure uniformly over the entire active areas of the sheets in the stack, said spring plate being constructed to tend to bend but being more or less flattened in service with the rest of the clamping` means while maintaining the desired compression for various lengths of the stack under service conditions.

33. In an electrical condenser, the combination with a stack of dielectric and conducting sheets, of clamping means arranged to subjectthe stack to high pressure from end to end and hold the sheets therein in intimate contact with one another throughout their active areas during service, said means including a principal portion of metal extending with metallic continuity from one end of the stack to the other; and-- said means including also a metal spring plate arranged transversely ofl one end of the stack and parallel to the sheets therein, said spring plate and the rest of the clampin means being constructed and arranged to distribute the pressure uniformly over the areas of the sheets in the stack, and said plate being constructed to tend to bend but being more or less flattened in service with the principal portion of the clamping means to maintain the desired pressure at various lengths of the stack under service conditions.

34. In an electrical condenser, a stack of conductors and dielectrics, pressure plates upon opposite ends of the stack, one at least of which is springy, and means adjustably connecting said pressure plates whereby an difference of potential, and a clamp therefor having pressure plates at the opposite ends of the stack, one at least of said plates being springy, and means insulating the opposite ends of the stack from each other.

36. In an electrical condenser, the combination with a stack of sheets constructed to have a difference of potential between the conducting sheets Aat opposite ends of the stack; of a metal casing enclosing the stack, a spring metal clamping plate extending over an end of the stack inside the metal casing; insulation between the clamping plate and thel stack; and means for flexing the clamping plate to compressthe stack.

37. Inv an electrical condenser, a stack comprising alternate sheets of foil and dielectric in lintimate contact, and clamping -means for maintaining said intimate'contact and including a spring plate arranged to have its surface facing an lend of the stack and held under stress exerting a resilient pressure over the active area of opposite ends of the stack.

38. In an electrical condenser, a stack comprising alternate sheets of foil and dielectric in intimate contact and clamping means for maintaining said intimate contact and including a vsprnig plate arranged to have its surface facing an end of the stack and held under stress, tending to assume a .curved condition and exerting a resilientpressure over the active area of opposite ends of the stack.

39. In an electrical condenser, a stack comprising alternate sheets of foil and dielectric and clamping means exerting uniform pressure over opposite ends of thestack and including a spring plate arranged to have its surface facing an end of the stack and held under stress whereby said pressure is maintained resiliently.

. In testimony whereof I have signed my name tov this specification.

WILLIAMl H. rnrEss. 

